We present evidence for the presence of fibronectin-binding adhesins in Borrelia burgdorferi and several other Borrelia species. Immunofluorescence studies show that plasma fibronectin is bound uniformly over the cell surface of free swimming B. burgdorferi. In addition, the spirochetes are able to bind to plasma fibronectin-coated microwel1 plates, an interaction that is inhibited by anti-fibronectin antibody as well as exogenous plasma fibronectin. Taken together, the data suggest that fibronectin binds to the surface of the spirochete. On Western-blot-like assays, B. burgdorferi and some B. afzelii strains express a major fibronectin-binding adhesin with an approximate molecular mass of 52 kDa. In addition, several other major fibronectin-binding adhesins were found in B. hermsii )26, 31, 33, 39, 46, 54, and 58 kDa) and B. turicatae (39, 41, 45, 50, 56, 59 and 66 kDa). Preliminary evidence suggests that fibronectin (and fibronectin-binding adhesins) may play a role as a molecular bridge between the spirochete and other components of the extracellular matrix.